PC Based Spectrum Analyzer

Team May00-04 Advisors: Dr. Dickerson & Dr. Black Client: Lee Moore, ISU BSEE 1982 TERADYNE, North Reading, MA

Team Members Chris Van Oosbree, CprE

Emmetsburg, Iowa

Fazal Baloch, EE

Balochistan, Pakistan

Yew-Kwong Soo, EE

Kuantan, Malaysia

Wee-Liat Tay, EE

Taiping, Malaysia

Walter Wedan, EE

Duluth, Minnesota

Background •What is a spectrum analyzer?

•Time domain vs. Frequency domain •Fourier Transform •Applications •TERADYNE J750

Spectrum Analyzers •Display a time domain signal in the frequency domain •Make noise measurements of a signal. •How “pure” is the signal?

Oscilliscopes display signals in the

time frequency

domain

Time Domain vs. Frequency Domain

Fourier Transform

Time Domain vs. Frequency Domain

Harmonic Distortion Fundamental Signal with Harmonic Distortion 2 nd Harmonic

Harmonic Distortion Fundamental Signal with Harmonic Distortion 2 nd Harmonic

Teradyne’s INTEGRA J750 • • • Automatic VLSI test platform Up to 1024 I/O pins Typically used on semiconductor fabrication lines VLSI (Very Large Scale Integration) is the art of putting 100,000+ transistors onto a single integrated circuit

J750 Technical Approach Input Module/Filters Digitizer Card Analyzer PC Control PC • Capture sinusoidal signals • Display spectrum (Fourier transform) of signal • Measure

total

harmonic distortion • Controlled by another PC

HP 33120A Technical Approach Input Module/Filters Digitizer Card Analyzer PC • Capture sinusoidal signals • Display spectrum (Fourier transform) of signal • Measure

total

harmonic distortion

Technical Approach • Software based approach – LabWindows/CVI used for coding • High speed digitizer card • Filters to “condition” the source signal • Filter calibration • Design of input module

Requirements • Measure THD of a sinusoidal source at 3 frequencies – 10 kHz – 100 kHz – 10 MHz • THD measurements up to the 3 rd harmonic • Noise floor is –135 dB below the the fundamental • 2 update rates • Free run mode • Slow / lowest noise

Software Overview • Have digitizer card capture signal • Compute Fourier Transform of the signal • Display signal spectrum • Compute and display THD • Display options – Harmonic Spectrum – Spectrogram

Screen Shot

Configuration Options • Sampling Rate • Windowing • Number of samples used in Fourier analysis – More samples = Better accuracy – Less samples = Faster computation • Averaging – To reduce effects of noise – Slower computation

Analyzer PC

• Dell Precision 410 • Dual 600 MHz Pentium III Processors • 1 Gigabyte RAM

Digitizer Card

• Sampling rate vs. Voltage Resolution • Faster sampling rate means lower resolution • Transtech ICS-650 • Available off the shelf • 12 bit resolution • Greater number of bits increases “horizontal” resolution • 65 MHz sampling rate • 3 rd harmonic of a 10 MHz signal is 30 MHz. Must sample at at least 60 MHz (Nyquist)

Signal Filtering

Notch

•Limited resolution of the digitizer card •Attenuating the fundamental makes the harmonics more “visible” •The harmonics are attenuated slightly.

•Must be compensated for in software

Spectrum Reconstruction

• The software filter is a discrete representation of the analog filter’s frequency response. • The software filter is calibrated to match the analog filter’s response during FILTER CALIBRATION.

Filter Calibration Procedure

User interface allows the user to specify: • Filter Notch Frequency 10kHz, 100kHz, 10MHz • Calibration Type Harmonic, Full Sweep • Sample Window Length Number of discrete frequency elements for the sample window, resultant DFT, and software filter 1024 – 16384

Filter Calibration Procedure

• With the filter in-line generate a sine wave of known amplitude.

• Find amplitude of filtered sine wave • Divide this amplitude by the amplitude of the unfiltered sine wave • Convert to decibels – 20 log 10 (filtered / unfiltered) • Increase sine wave frequency and repeat.

Spectrum Reconstruction

•Compensating for the filter in software ensures that analysis results are correct

Filter Design • Twin-T network design is used for building filters attenuating signals at 10kHz and 100kHz • Twin-T has simple basic design that gives good attenuations • A 5 th order Chebyshev Band Stop Filter will be tested for attenuation of signals at 10MHz

Problems • The sensitivity of the Twin-T filter • Twin-T filter unsuitable for attenuating high frequencies such as 10MHz • Getting the components for the filter

Schematic TWIN-T filter

Schematic (cont.)

Filter Response Attenuation at 10kHz

Filter Response (cont.) Attenuation at 10MHz

Input Module • Vishay Siliconix DG534A • 4x1 Multiplexer • Wide Bandwidth 500MHz • Controlled via Parallel Port

Input Module Block Diagram 10kHz Filtered Input 100kHz Filtered Input 10MHz Filtered Input Unfiltered Input Vishay DG534A Selected Output Parallel Port Control

Fazal

Personnel Effort Budget

Personnel Original Estimated Effort Revised Estimated Effort

100 hours 75 hours Soo Tay Chris Walter

Total Estimated Effort

100 hours 100 hours 100 hours 100 hours

500 hours

70 hours 70 hours 125 hours 75 hours

415 hours

Item

Computer Digitizer Card

Financial Budget

Original Estimated Cost

$ 6,000.00

Revised Estimated Cost

$ 6,500.00

$ 4,000.00

$ 5,500.00

Software Project Poster Programming Books $ 1000.00

$ 100.00

$ 0.00

$ 0.00

$ 122.00

$ 70.00

GPIB Card

Total Estimated Cost

$ 0.00

$ 11,000.00

Funds provided by TERADYNE $ 800.00

$ 12,992.00

Problems Encountered • Filter and input module parts were never ordered because of long lead time • Original specification was for VisualBasic, chose LabWindows instead

Future Work • Control via external PC • Faster signals (up to 100 MHz) • Build filters and input module

Lessons Learned • Order parts early • Meet often with advisor • Team mailing list • Reduce scope of project if necessary

Milestone Summary • Successfully wrote code to control digitizer card • Analyzer software is finished and being documented • Filter calibration software is finished

Questions ???